In the desire to increase production, quality and competitiveness, people have sought many means to hold a part or parts so that it can be machined accurately and quickly. Most of the time the industry uses a vice, collets, chucks, over center clamping or custom designed fixtures. While these devices have been developed to hold parts securely and accurately, loading only one part at a time often severely limits machine and operator efficiency.
Perhaps one of the significant problems that faced in this field is the fact that CNC machining is a relatively new field and though some work has been done in the field of fourth axis work holding, relatively little has been done in work holding in horizontal or vertical machining centers. In an effort to increase operator and machine efficiency, those in the field often secure multiple collets, vices, over center locking systems and a variety of other devices to the machining table to hold multiple parts. While this approach may provide some improvement, the loading and unloading of parts is usually done with the machine turned off and therefore limits efficiency for both the machine and for the operator.
A pallet system is sometimes used. Multiple holding devices are sometimes secured to two pallets in an identical manner allowing parts to be loaded on one pallet outside of the work environment while the parts on the other pallet are being machined. This method may improve efficiency to some degree but problems of efficiency remain. This method often requires manual tightening or releasing of multiple screws or other mechanical devices. This can be time consuming and inefficient for the operator. It can also lead to physical stress and carpal tunnel concerns which also negatively impact efficiency. On some jobs, the loading and unloading of the parts may take longer than the machine cycle time. The machine would then be waiting for the operator and therefore not operating as efficiently as possible. These holding devices can also tend to be oversized and bulky limiting the number of them that fit into the work area and thereby limiting the number of parts that can be loaded at a particular time. Change over from one part to another can also be time consuming.
In addition to these efficiency problems, this pallet approach can create other problems. When vices are used, accuracy may be hard to maintain due to inherent problems with vices. The security of the part may be an issue if the size of the part varies and you are holding more than one part; one or more parts may be loose when the others are tight. When custom jaws are used the cost may be high and accuracy can still be an issue with duplication for multiple holding devices and multiple pallets.
Attempts to solve problems in this field include U.S. Pat. No. 3,632,122. This device utilizes hydraulic pressure to clamp parts in collets and releases them when the pressure is removed. This invention solves some of the accuracy and security problems stated above. If two of these units were bolted to two pallets in a pallet system, many of the problems of efficiency stated above could be solved. One type of problem with this device, which is solved by the current invention, is the very limited scope of its application; it is very limited in the size and shape of the parts that it can hold, the angles at which it can hold them, and the number of parts it can hold at a time. From some perspectives, this device can hold a very limited diameter and shape of parts—only those parts that can be held in the particular collets built into the system (3C, 5C, etc.). The part may also need to be a certain length. If it is too long, the device may not work at all or quality may be negatively impacted. It is not fully adaptable for other applications such as clamping by pushing, pulling for sideways movement, clamping in “V” blocks, or many other methods of holding. This device is also very limited when holding parts in the horizontal plane and doing cross work because of the distance from the top of the fixture to the centerline of the collet. This distance can require excessively long tooling or extension of the part a significant distance from the collet, either of which may impact rigidity and accuracy. In some situations, the bottom row cannot be accessed to do cross work because the top row is in the way. This can significantly limit the number of parts that can be machined per cycle. The device can also be limited to holding parts vertically or horizontally and may not be efficiently machined in other planes.
In an effort to overcome some of these limitations, some people create custom fixtures to hold the parts they manufacture. They utilize collets, vices, over center clamping and a variety of other devices. More recently, modular hydraulic devices have become available to automate the clamping and unclamping. This approach does solve some of the problems but it may also create problems. One problem is the time required to create custom holding devices. The excessive time required often does not meet the demands of a quick response marketplace. The manufacturer is therefore often faced with the choice of inefficient and expensive setup or inefficient and expensive run time. Another problem is that run efficiency can be rather limited. Custom fixtures are usually bulky limiting the number of parts that will fit in the work area and therefore the number that can be loaded at a time. Self-made fixtures also tend to be inaccurate affecting quality and also creating inefficiencies. Many fixtures use mechanical clamping which can mean tightening screws or over center clamps. This can be time consuming and labor intensive. Efficiencies are also lost due to operator fatigue. In addition, often the parts are not held securely creating quality, rework and safety issues. Screws, which are often used in holding parts, can tend to mar the part or collapse a thin walled part affecting quality and therefore affecting efficiencies. Unless two identical fixtures are made, the parts can need to be loaded and unloaded in the work area so the load time can be slow and labor intensive and therefore machine down time can be lengthy. When two identical fixtures are made and one scrapped out, you often need to make both over again to get the precision needed. Sometimes the design doesn't work as planned. The initial cost of custom fixture making can be high because it can require significant amounts of time from highly skilled design personnel. It can also require expensive materials and services since the materials are usually purchased in small quantities and the special services are preformed in small quantities (heat treating, anodizing, grinding, etc.). The on-going costs can also be high. As mentioned, fixtures are often designed and built for a specific part. When a new fixture is desired for a different part it can become necessary to start over again. Fixtures may tend to become similar but are often not interchangeable; they are not easily adaptable to other parts. They often become obsolete because of minor print changes or need major rework. The cost of starting over is, of course, very high. The inventory of fixtures can become extensive, taking up large amounts of shelf space. They can be expensive to maintain especially if they are lost and damaged.
As to both the application to the CNC machining center and to machining in general, the present invention discloses techniques that overcome virtually every one of the previous problems in a practical fashion. It provides to the manufacturing industry the opportunity to significantly improve both setup and run time efficiencies, reduce operator fatigue and carpel tunnel concerns, and maintain or improve quality and safety.